The following abbreviations are used in the application documents of the present application.    ALP: alkaline phosphatase    αMEM: minimum essential medium alpha medium    BMP-2: bone morphogenetic protein-2    BSP: bone sialoprotein    COLI: type I collagen    FBS: fetal bovine serum    GAG: glycosaminoglycan    GlcN: glucosamine    GlcA: glucuronic acid    Hep: heparin    HexA: hexuronic acid    HS: heparan sulfate    IdoA: iduronic acid    PCR: polymerase chain reaction    RT-PCR: reverse transcription PCR    2DSH: 2-O-desulfated Hep (2-O-desulfated heparin) (a substance in which a 2-position hydroxyl group of HexA residue in Hep is desulfated)    6DSH: 6-O-desulfated Hep (6-O-desulfated heparin) (a substance in which a 6-position hydroxyl group of GlcN residue in Hep is desulfated)    NDSH: N-desulfated Hep (N-desulfated heparin) (a substance in which a 2-position amino group of GlcN residue in Hep is desulfated)
Background art of the present invention is described in the following.
In Patent Reference 1, an intercellular connection promoter comprising, as the active ingredient, GAG which has a sulfate and a disaccharide repeating structure consisting of a HexA residue and a GlcN residue as the basic structure, wherein said GAG comprises the HexA residue in which a 2-position hydroxyl group is not esterificated with sulfuric acid or the GlcN residue in which a 2-position amino group is not sulfaminated is described.
In Patent Reference 2, an intercellular connection suppressor comprising, as the active ingredient, GAG which has a sulfate group and a disaccharide repeating structure consisting of a HexA residue and a GlcN residue as the basic structure, wherein said GAG contains the Glc residue in which a 6-position hydroxyl group is not esterificated with sulfuric acid is described.
Patent Reference 3 discloses a certain species of desulfated Hep, and discloses an accelerator of a basic fibroblast growth factor activity comprising the same as an active ingredient and a composition which comprises the same and the basic fibroblast growth factor and accelerates activity of the basic fibroblast growth factor upon the cell growth.
Patent Reference 4 discloses a hyaluronic acid fraction having a bone formation activity and a molecular weight of from 20 kDa to 40 kDa.    Patent Reference 1: JP-A-2003-113090    Patent Reference 2: JP-A-2003-119146    Patent Reference 3: International Publication No. 96/01278    Patent Reference 4: Japanese Patent No. 3333205
However, there is no disclosure or suggestion that a GAG or a salt thereof, which has a sulfate group and a disaccharide repeating structure consisting of a HexA residue and a GlcN residue as a basic structure, wherein one or less of the position among a 2-position hydroxyl group of the HexA residue, a 6-position hydroxyl group of the GlcN residue and a 2-position amino group of the GlcN residue in the basic structure does not have the sulfate group, by itself has activity of directly accelerating hard tissue formation, accelerating differentiation of a cell and increasing ALP activity of the cell.